When a magnetic resonance imaging apparatus is used to obtain an image, images showing the contrast between various tissues can be obtained by changing the parameters of the time of echo (TE), the time of repetition (TR), and performing image calculations. The methods of obtaining an image having such contrast include the Dixon method. The Dixon method is a method of obtaining a water/fat separated image by utilizing the phase change of water MR signals and fat MR signals in one region.
Recently, in clinical settings, opportunities for imaging both right and left crural regions at the same time, or of imaging a transverse cross section of the brain-basilar region of the head, or of imaging a coronal cross-section of the abdomen, are increasing in diagnosing from a water/fat separated image. A conventional technique of accurately obtaining a water/fat separated image, when the imaging region is separated into a plurality of island-like portions because the object to be examined includes a plurality of spatially-separated portions, or the object includes portions that product no signals, such as those of air, is disclosed in “A New Two-Dimensional Phase Unwrapping Algorithm for MRI Images”, by M. Hedley and D. Rosenfeld, in Magnetic Resonance in Medicine, Vol. 24, 177-181 (1992). According to this technique, when there are two island-like regions, only the phases of the points of the first region and the second region closest to each other are simply compared. However, with such a technique, since it is difficult to obtain a desired image of a portion where there is a local rapid change of phases, or where the island-like regions are greatly separated, the water image and the fat image cannot be separated, and portions where the water signals are extracted and portions where the fat signals are extracted are mixed up in one image.